Camera apparatus for controlling diaphragm and shutter speed

ABSTRACT

An exposure control system for use in photographic apparatus which provides automatic adjustment of the exposure aperture in response to a signal from a photoresponsive member and then actuates a shutter mechanism to make an exposure for an interval determined by a timing circuit as a function of the aperture adjustment and the signal from the photoresponsive member. Preferably, the system includes indicator means controlled by the photoresponsive member to provide an indication of low light conditions and of the termination of the exposure interval.

United States Patent Metzger et al. 14 1 May 16, 1972 54] CAMERAAPPARATUS FOR 3,427,941 2/1969 Metzger ..95/64 D x NT LLI DI H AND3,292,516 12/1966 Sato et al. 3,464,332 9/ 1969 Davison et al. ..95/64 DSHUTTER SPEED 3,547,018 12/1970 l-laberle ..95/10 C [72] Inventors:Lenard M. Metzger; Richard J, Bresson 3,554,104 1/l97l Winkler ..95/l0 Cboth of Rochester, N.Y.; Randall T. Mc- Conaughey, Boulder, Colo.Primary Examiner-Samuel S. Matthews Assistant Examiner-Michael L.Gellner [73] Asslgnee: :i' Kodak Company, Rochester Att0rney-Robert W.Hampton and William F. Delaney, Jr.

221 Filed: June 22, 1970 [571 ABSTRACT An exposure control system foruse in photographic apparatus [2]] Appl' which provides automaticadjustment of the exposure aperture in response to a signal from aphotoresponsive member [52] 11.8. Cl. ..95/10 CD, 95/10 CT, 95/64 D nhen actuates a sh r mechanism to make an exposure 51 m 3| ;03 9 07, 0317 03 for an interval determined by a timing circuit as a function of[58] Field of Search ..95/10 C, 64 D the aperture adjustment and theSignal from the p p sive member, Preferably, the system includesindicator means 56] References Cited controlled by the photoresponsivemember to provide an indication of low light conditions and of thetermination of the ex- UNITED STATES PATENTS P interval 3,538,82311/1970 Wagner ..95/10 C 2 Claims, 2 Drawing Figures 112 7 g A94 1 w J92 '06 [108 g 98 7 10 P'ATENTEMAHem 3.662.659

SHEET 1 BF 2 FIG.|

LE NARD M. METZGER RICHARD J. BRESSON RANDALL I MCCONA INVENTORATTORNEYS SHEEI 2 OF 2 RANDALL T. MCCONAUGHEY INVENTORS BY z/iflzm 9w W054.

ATTORNEYS I I I P'A'TENTEDIM 16 m2 CAMERA APPARATUS FOR CONTROLLINGDIAPHRAGM AND SHUTTER SPEED CROSS-REFERENCE TO RELATED APPLICATIONSReference is made to commonly assigned, copending U.S. application, Ser.No. 823,789, filed in the names of Daniel E. Carter et al. on May 12,1969, and US. Pat. application, Ser. No. 823,426, filed in the names ofDaniel E. Carter et al. on May 9, 1969.

BACKGROUND OF THE INVENTION This invention is related to exposurecontrol systems for use in photographic apparatus, such as cameras, andmore particularly to an exposure control system in which the exposureaperture and the exposure time are automatically controlled inaccordance with the level of scene illumination.

In previous exposure control systems in which an automatic control isprovided for determining the length of an exposure interval, provisionhas been made for the automatic adjustment of the exposure apertureimmediately preceding initiation of the exposure interval in accordancewith anticipated scene light. Such a system in which the exposure speedis controlled in response to an electronic timing circuit, and theexposure aperture is adjusted to one of a plurality of predetermineddiscrete aperture sizes by an automatic control system is shown in US.Pat. No. 3,464,332, issued to Davidson et al on Sept. 2, 1969. Thesystem disclosed in that patent preselects one of a plurality ofpredetermined aperture stops by means of a plurality of blades havingdifferent aperture sizes to provide a gross adjustment according to thelevel of anticipated scene illumination prior to initiation of theexposure interval. However, such diaphragm control systems provide onlydiscrete aperture stops and do not provide compensation for focusadjustment changes after the aperture has been set but prior toinitiation of the exposure interval. Moreover, such systems employmechanical apparatus requiring considerable space, which is particularlyundesirable in view of the recent trend toward miniaturization ofcameras.

Another prior art exposure control system including means forautomatically adjusting the exposure aperture and shutter speed is shownin British Pat. No. 1,093,235, published on Nov. 29, 1967. The systemdisclosed in that patent includes a diaphragm control member that isreleasable by the shutter actuation lever for rotation under theinfluence of a spring bias until an electronic trigger circuit actuatesa solenoid to stop the member at a position in which the exposureaperture is a size suitable for the level of scene illumination. Themechanical apparatus employed in this system requires numerous movingparts which adds to its assembly costs and space requirements. Forexample, this diaphragm mechanism includes apparatus for resetting thecontrol member after each exposure. Accordingly, such an exposurecontrol system is not particularly well suited for miniaturized cameras.

Also known in the prior art are electronic shutter timing systems whichinclude indicator means for providing a signal indicating low scenelight, so that an operator knows when to use an artificial light sourceor to ensure camera steadiness for long exposures. In addition,electronic shutter timing systems are known which include means forindicating when the shutter is open, so that an operator avoids movingthe camera during a long exposure, and particularly to avoid a mistakenassumption by an operator that the exposure has terminated.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved automatic exposure control system requiring few mechanicalparts, which automatically adjusts an exposure aperture prior toinitiation of an exposure interval, and then controls the length of theexposure interval by means of a time-delay circuit in accordance withthe level of scene illumination.

It is another object of this invention to provide an improved indicatorsystem incorporated in such an exposure control system for providing alow light signal when the scene illumination is below a predeterminedlevel, and for providing a shutter-closed signal immediately upontermination of an exposure interval.

It is a further object of this invention to provide such an improvedindicator system including a single signal means which is actuated priorto an exposure interval when low light conditions exist, and which alsois activated in synchronization with the termination of the exposureinterval to indicate when the shutter has closed.

An exposure control apparatus according to the preferred embodiment ofthe present invention comprises a photoresponsive member for providingan electrical output signal related to the level of illuminationincident thereon from an object scene, a diaphragm member associatedwith a magnetic member for movement to any .position along a path tovary the size of an exposure aperture, a diaphragm control circuitincluding a drive coil having oppositely poled inputs for moving themagnetic member for adjusting the diaphragm member in response to theoutput signal of the photoresponsive means, shutter means actuatable toinitiate an exposure interval after adjustment of the diaphragm memberand a time-delay circuit for establishing the length of the exposureinterval as a function of the diaphragm adjustment and the output signalfrom the photoresponsive means.

Preferably, an exposure control apparatus according to this inventionincludes indicator means associated with the photoresponsive member forproviding a signal when the level of scene illumination is below apredetermined value, and for providing a signal upon termination of anexposure interval. The indicator means according to the preferredembodiment of the invention is associated with the time-delay circuitand an indicator-control trigger circuit that is activated when thesignal from the photoresponsive member is below a predetermined value,in such a manner that the indicator is activated prior to an exposureinterval when the level of scene illumination is below a predeterminedlevel, and upon termination of the exposure interval to indicate whenthe shutter has closed.

The diaphragm control system according to the preferred embodiment ofthis invention is adapted to move the diaphragm member to any positionalong a path to vary the size of the exposure aperture by means of drivecoil means activated by the diaphragm control circuit which selectivelyenergizes the coil means in response to the level of scene illumination.Preferably, the diaphragm control circuit comprises a differentialamplifier. This arrangement provides an analog adjustment of thediaphragm with a few moving parts, and it permits adjustment of thediaphragm to compensate for focusing adjustments made after the exposurecontrol system has been activated, but prior to initiation of theexposure interval in cameras of the type in which the photocell receiveslight transmitted through the camera objective.

An exposure control apparatus according to the present invention isadapted for exposures in artificial light, as well as in ambient scenelight. For photographic exposures made in artificial light, such as witha flashbulb, the exposure aperture can be adjusted according to thefocus setting, or it can be adapted for automatic adjustment to apredetermined aperture setting. Preferably, insertion of a fiashbulbinto a camera socket automatically disables the diaphragm controlcircuit and mechanically couples the diaphragm means with a focusadjusting means on the camera, since light from an artificial source isa function of the intensity of the source as well as the distancebetween the object scene and the light source which is usually at thecamera.

BRIEF DESCRIPTION OF THE DRAWINGS The detailed operation of thepreferred embodiment of this invention can be described more completelywith reference to the accompanying drawings in which:

FIG. 1 shows an exploded perspective view of the preferred embodiment ofthe shutter and diaphragm mechanisms of an exposure control apparatusaccording to the invention; and

FIG. 2 shows a circuit diagram for controlling the mechanisms shown inFIG. 1, including a time-delay circuit for controlling the exposuretime, a diaphragm control circuit and an indicator-control triggercircuit according to the preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION An exposure control systemaccording to the present invention includes an adjustable diaphragmmechanism including a member movable to any position along a path forvarying an exposure aperture in accordance with the level of scenelight, and a shutter mechanism controlled by an electronic timedelaycircuit that establishes the length of an exposure interval. Thetime-delay circuit preferably is of the integrating type forcontinuously measuring the total accumulated amount of light energyimpinging on a photoresponsive member in the timing circuit. After thediaphragm mechanism has been actuated to adjust the exposure aperture inaccordance with the level of scene illumination, the shutter mechanismis then actuated to initiate an exposure interval under the controlofthe electronic timing circuit that terminates the exposure interval inaccordance with the exposure aperture adjustment and in accordance withthe amount of illumination actually received during the exposureinterval by the photoresponsive member in the timing circuit. Theshutter timing circuit can compensate for the exposure aperture setting,for example, by adjustment of an electrical parameter of the timingcircuit to vary its time constant, or preferably by varying the apertureof the photoresponsive member used in the timing circuit in accordancewith the adjustment of the exposure aperture by the diaphragm mechanism.

Referring now to the accompanying drawings, FIG. 1 shows an exposurecontrol apparatus according to a preferred embodiment of the invention,including an objective for forming an image on photographic film F, atwo-bladed diaphragm mechanism 12 for establishing a variable exposureaperture in alignment with the optical axis 14 of the objective, and atwobladed shutter mechanism 16 for initiating and terminating anexposure through the objective.

The diaphragm mechanism 12 includes a pair of blades 18 and 20 that areslidably mounted upon suitable support means (not shown) for equal andopposite movement relative to the lens axis 14. Each of these blades hasa tapered aperture 22 and 24, respectively, overlying each other todefine an exposure aperture 25 aligned with the optical axis 14. Theapertures 22 and 24 are disposed with their tapered portions extendingin opposite directions with respect to each other along the line oftravel of the two diaphragm blades, such that opposite movement of theblades 18 and 20 will enlarge or diminish the size of the exposureaperture 25. Each of the blades 18 and 20 also has a second taperedaperture 26 and 28, respectively, similar to the tapered aperture 22 and24, overlying each other to define a second variable aperture 29overlying a photocell 30. A lens 32 having an optical axis 33 ispositioned to form an image of an object scene on the photocell throughthe variable photocell aperture 29. Thus, opposite movement of thediaphragm blades 18 and 20 will result in a variation of the size of theaperture 29 over the photocell 30 simultaneously with the variation ofthe size of the exposure aperture 25. The diaphragm blades 18 and 20 areeach connected to opposite ends of an armature 35 rotatably driven by anelectro-mechanical transducer 36, which in this embodiment is aservomotor having input leads 38, and 42. The operation of thisservomotor will be described in further detail with respect to thecircuit in FIG. 2 below.

The shutter mechanism 16 is a conventional two-blade system, which isshown in FIG. 1 in its cocked" position preparatory to actuation toeffect an exposure. The shutter mechanism includes a pair of shutterblades 44 and 46 which are slidably mounted upon suitable support means(not shown) for movement relative to the exposure aperture 25.

When the blade 44, which is the "opening" blade in this embodiment, isin its cocked position shown, it is retained against the bias of aspring 48 by a latch member 50 which is biased by a spring 52 intolatching engagement with a detent 53, in which position the latch memberengages a pin 54. The opening" blade 44 has a second detent 56positioned to engage a detent 58 on the blade 46, which in thisembodiment is the closing blade. Thus, blade 46 is retained in itscocked position against the bias of a spring 60 by the interengagementof the detents 56 and 58. In their respective cocked positions theopening" blade 44 is retained in a covering relationship with respect tothe exposure aperture 25, and the "closing" blade 46 is retained in anuncovering position with respect to the exposure aperture. When theblades are in their respective cocked positions, the spring 48 urges theopening" blade 44 to an uncovering position with respect to the exposureaperture, and the spring 60 urges the closing blade 46 to a coveringposition over the exposure aperture.

The closing" blade 46 also includes a second detent 66 having a camsurface 68 adapted to engage a retaining lever 70 pivotally mounted on apin 72 and biased by spring 74 in a counterclockwise direction intoengagement with the detent 66. The opposite end of lever 70 is connectedto an electromagnetic keeper 76 positioned adjacent a pole of anelectromagnet 78 when the shutter blade 46 is in its cocked position.The electromagnet 78 is energized and de-energized by an electronictiming circuit discussed in more detail below with respect to FIG. 2.When the electromagnet is energized it holds the lever 70 in itsretaining position shown in FIG. I, to hold the blade 46 in itsuncovering position when the detents 56 and 58 become disengaged uponrelease of the opening" blade for movement to its uncovering position,thereby initiating an exposure interval. Thereafter, when theelectromagnet 78 is de-energized, the bias of spring 60 overpowers thebias of the weaker spring 74 to cause the detent 66 to cam the lever 70in a clockwise direction, thereby releasing the closed blade formovement to a covering position with respect to the exposure apertureand terminate the exposure interval.

For actuation of the shutter mechanism 16 to effect an exposure, it isprovided with a shutter actuation button 80 mounted in an externalposition on the camera so as to be available to a camera operator. Thebutton 80 is mechanically coupled to a rod or bar 82 that is slidablymounted on mounts (not shown) for movement toward engagement with adetent 84 on shutter latch lever 50, when the shutter actuation button80 is depressed. Initial movement of the slide bar 82 causes aprojection 86 thereon to engage a contact of a normally open switch S1,thereby causing the switch to be closed. An actuating member 87 on aslide bar 82 then engages simultaneously movable contacts of a pair ofswitches S2 and S3, thereby opening the normally closed switch S2 andmoving the flexible spring contacts a against its bias out of engagementwith fixed contact b and into engagement with contact 0 of the switchS3. Continued movement of the slide bar 82 causes it to engage thedetent 84 and rotate the latch 50 in a clockwise direction out ofengagement with the detent 53 on the opening" shutter blade 44, therebyreleasing the blade for movement under the influence of spring 48 to anuncovering position with respect to the exposure aperture 24 to therebyinitiate an exposure interval. When the opening" blade 44 moves awayfrom its cocked position, it moves out of engagement with one of thecontacts of a normally closed switch S4, thereby causing that switch toopen.

As shown in FIG. 1 the shutter mechanism is in its cocked positionpreparatory to actuation of the shutter blade to effect exposure by theoperator. When the camera operator depresses the shutter actuationbutton 80, switch S1 closes energizing the exposure control circuitshown in FIG. 2, switches S2 and S3 are then actuated, and then latch 50is rotated clockwise to release the opening blade for movement to itsuncovering position with respect to the exposure aperture to therebyinitiate an exposure interval and open timing switch S2. When shutterblade 44 moves to its uncovering position, the detent 56 moves out ofengagement with the detent 58 on the closing shutter blade 46. However,the electromagnet 78 is energized by the exposure control circuit whenthe switch S1 is closed, as described below, and latch 70 is held in itsretaining position by the electromagnet to prevent the closing" blade 46from moving away from its unblocking position. After a period of timedetermined by the circuit in response to the level of illuminationdetected by a photoresponsive member in the circuit, the electromagnet78 is de-energized to release the closing blade 46 for movement to itsblocking position to terminate the exposure interval. Following anexposure the shutter blades can be returned to their cocked positions bymovement of a cocking lever 62 to engage a detent 64 thereon with thedetent 56 on the opening blade to move the blades back to their cockedposition, shown in FIG. 1.

As described above when the shutter actuation button 80 is depressed,switch S1 is closed prior to actuation of switches S2 and S3 and priorto the release of the opening blade. Closure of the switch S1 energizesthe circuit, shown in FIG. 2, from a battery source 90. Because of theparticular bias voltages established as a result of the closing of theswitch S1, a first trigger circuit, indicated as block 92 having anoutput terminal 93, is energized into a conductive state almostinstantaneously. When the trigger circuit 92 is in a conductive state,it causes a current through a coil 94 of the electromagnet 78 to retainthe closing shutter blade 46 in its initial uncovering position afterthe opening" blade 44 has moved away from its initial position.

Closure of switch S1 also activates the diaphragm control networkthrough the closed switch S2 and the engaged contacts a and b of switchS3. In the position shown switch S3 connects the photoconductive cell 30in series with a variable resistance 96, which are connected throughswitch 81 across the battery source 90 to form a voltage divider circuitthat provides a voltage at a junction 98 that is functionally related tothe level of illumination incident on the photo-resistor 30. Connectedto the junction 98 is the input terminal 38 of an aperture controlcircuit, shown as block 100, which is energized when switch S1 is closedto actuate oppositely poled drive coils 102 and 104 of servomotor 36according to the input voltage. The aperture control circuit can be adifferential amplifier, such as disclosed in commonly assigned,copending U.S. Pat. application, Ser. Nos. 823,426 or 823,789, filed inthe names of Daniel E. Carter et al. on May 9, 1969 and May 12, 1969,respectively. Other examples of control circuits that can be used tocontrol the aperture according to this invention are disclosed in U.S.Pat. No. 3,427,941 issued to L. M. Metzger on Feb. 18, 1969. When switchS1 is closed, the armature 35 of the servomotor 36 is rotated by thedrive coils 102 and 104 to adjust the diaphragm blades 18 and 20 inrespectively opposite directions to increase or decrease the exposureaperture to a size suitable for the level of illumination incident onthe photoresistor 30.

Also connected to the junction 98 is an input terminal 106 of a secondtrigger circuit, indicated as a block 108, for controlling an indicatorcircuit. The output terminal 110 of the trigger circuit 108 is connectedin series with an indicator lamp 112. The trigger circuit 108 is adaptedto be switched between a conductive state. when the voltage at thejunction 98 is below a predetermined value, and a nonconductive statewhen that voltage is above that predetermined value. Thus, the lamp 112is energizable through the trigger circuit 108 to indicate low scenelight conditions.

Further depression of shutter actuation button 80 causes the member 87to open the switch S2 and actuate the switch S3 to engage the contact awith contact c, thereby disconnecting the aperture control circuit andthe indicator control trigger circuit 108 from the battery source 90,and connecting the photoresistor 30 in series with a capacitor 120 tooperate as an integrating circuit. The trigger circuit v92 has an inputterminal 122 connected to the junction 124 between the photoresistor 30and the capacitor 120 which is grounded through a switch S4 so that thevoltage at the input terminal 122 of the trigger circuit 92 ismaintained at ground potential when switch S2 is closed. However, whenthe "opening" blade 44 is released from its cocked position, thenormally closed switch S4 is opened, as explained above, to cause thecapacitor 120 to be charged through the photoresistor 30 at a ratedetermined by the resistance value of the photoresistor. The photocell30 is disposed to receive light from a scene being photographed, so thatits resistance value is functionally related to the level of scenebrightness. Thus, when switch S4 opens, the voltage at 124 changes fromits initial ground potential to a predetermined value in a period oftime depending on the well-known time constant RC of the integratingcircuit, which is determined by the value of the capacitor 120 and thevalue of resistance 30 as established by the intensity of the light fromthe scene to be photographed. When the voltage at the input terminal 122of trigger circuit 92 reaches the predetermined value, the triggercircuit is caused to trigger or switch from its conductive state to itsnon-conductive state thereby causing the electromagnet 78 to rapidlyreduce its attracted force on the keeper 76 so as to release the blade46 permitting it to move to its blocking position under the biasingforce of spring 60. Thus the exposure interval is initiatedsimultaneously with the activation of the integrating circuit by theopening of switch S4, and it is terminated in response to triggering ofthe trigger circuit 92 after a period of time determined by theintegrating circuit according to the illumination incident on thephotoresistance 30. Therefore, the time between the release of the blade44 and the release of blade 46 is dependent upon the value of theresistant 30 in the integrating circuit, which is determined by thelevel of scene illumination incident thereon. Thus, a highlight levelunder very bright conditions produces a low resistance value ofresistance 30 and has a small RC time constant for the circuit whichresults in a short exposure time. Similarly a low level of scenebrightness produces a high resistance value and has a longer timeconstant for the circuit which results in a long exposure time under dimlight conditions.

Also connected to the output terminal 93 of the trigger circuit 92 isthe base of an NPN transistor T which has its collector-emitter pathconnected in series with the indicator lamp 112. When the switch S1 isclosed and the trigger circuit 92 is energized to a conductive state,the transistor T is biased to a nonconductive state so that theenergization of the lamp 112 is controlled only by the circuit 108 andfunctions as a low light indicator. When the trigger circuit 108 isdisconnected from the battery source by the switches S2 and S3, the lamp112 becomes inactive until the shutter control trigger circuit 92 isde-activated to a non-conductive state at the termination of an exposureinterval, at which time the transistor T is biased conductive to turnthe lamp on. Thus, the lamp 112 is off during the exposure interval, andit is turned on when the exposure interval is terminated. Accordingly,the transistor T functions as an or gate, so that the lamp 112 iscontrolled by either trigger circuit 92 or 108. This arrangement enablesthe lamp 112 to provide a low light signal, as well as a shutter-closedsignal.

Several types of well-known trigger circuits. are suitable for use asthe trigger circuits 92 and 108. A Schmidt trigger is one example ofsuch a typical prior art circuit. Further description of the details ofthe trigger circuits 92 and 108 is considered unnecessary, since theirstructure and switching function are well known in the prior art.

When an exposure is to be made with a photoflash apparatus, a switch S5is closed to connect a fixed resistor 126 in parallel with thephotoresistor 30. The fixed resistance 126 has a much lower resistancevalue than the photoresistor 30 in low light conditions, so that thetiming capacitor is charged principally through the resistance 126 toprovide a predetermined shutter speed for flash operation. Preferablythe switch S5 is actuated to close automatically in response toinsertion of a photoflash apparatus on the camera. Thus, when the switchS5 is closed, the aperture is set to a nominal position by the aperturecontrol circuit because of the fixed resistance thereby placed in thecircuit in parallel with the photocell. When focusing changes arerequired in a camera, it's possible to compensate for the focusingadjustment in the aperture setting, for example, by mechanicallycoupling the variable resistor 96 to the focus drive.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:

1. In a camera adapted to expose film to scene light, an exposurecontrol apparatus comprising:

a. photoresponsive means adapted to receive illumination from an objectscene for providing an electrical signal that varies as a function ofthe level of illumination incident thereon;

b. first electronic circuit means including said photoresponsive means,and adapted to switch between a first state when the scene illuminationexceeds a predetermined level, and a second state when the sceneillumination is below said predetermined value; I

. second electronic circuit means including said photoresponsive means,said second circuit means being activatable and adapted to switch from afirst state to a second state a period of time after activation thereof,the time period being established as a function of the level of sceneillumination;

d. shutter means for covering and uncovering the exposure aperture;

e. means for actuating said shutter means to uncover said exposureaperture to initiate an exposure interval;

f. means for activating said second circuit means substantially insynchronization with the actuation of said shutter means to uncover saidexposure aperture;

g. means for actuating said shutter means to cover said exposureaperture in response to switching of said second circuit from said firststate to said second state to terminate the exposure interval, so thatthe exposure interval is determined by said second circuit means as afunction of the level of scene illumination; and

h. an indicator circuit including signal means, said indicator circuitbeing connected to said first and second electronic circuit means, andadapted to activate said signal means when either of said circuits is inits respective second state to provide a signal prior to an exposureinterval when the scene illumination is below a predetermined value, andto provide a signal when an exposure interval is terminated.

2. In a camera adapted to expose film to scene light, an exposurecontrol apparatus comprising:

a. photoresponsive means adapted to receive illumination from an objectscene for providing an electrical signal functionally related to thelevel of scene illumination incident thereon;

b. diaphragm means for establishing an exposure aperture, said diaphragmmeans including a member movable to any position along a path to varythe size of the exposure aperture, and a magnetic member associated withsaid diaphragm member for movement therewith;

c. a diaphragm control circuit including said photoresponsive means, andincluding drive coil means having oppositely poled inputs, said coilmeans being associated with said magnetic member for moving saiddiaphragm member in a first direction along said path in response toenergization of one of said drive coil inputs and for moving saiddiaphragm member in the respectively opposite direction along said pathin response to energization of the other drive coil input, said circuitbeing activatable to selectively energize said coil means to adjust theexposure aperture to a size suitable for the level of illuminationincident on said photoresponsive means;

d. means for activating said diaphragm control circuit to adjust theexposure aperture; e. actuatable shutter means for covering anduncovering said exposure aperture;

f. a first trigger circuit including said photoresponsive means, saidcircuit being activatable and adapted to switch from a first state to asecond state a period of time after activation of said trigger circuit,the time period being established as a function of the position of thediaphragm member and the second electrical signal from saidphotoresponsive means;

g. means for actuating said shutter means to uncover said exposureaperture to initiate an exposure interval after activation of saiddiaphragm control circuit;

h. means for activating said first trigger circuit in synchronizationwith the actuation of said shutter means to uncover said exposureaperture;

. means for actuating said shutter means to cover said aperture inresponse to switching of said first trigger circuit to its second stateto terminate the exposure interval, so that the exposure interval isdetermined by said first trigger circuit as a function of the level ofscene illumination and the size of the exposure aperture;

. a second trigger circuit including said photoresponsive means, saidsecond trigger circuit being adapted to switch between a first statewhen said electrical signal exceeds a predetermined value, and a secondstate when said electrical signal is below said predetermined value; and

k. an indicator circuit including signal means, said indicator circuitbeing connected to said first and second trigger circuits, and adaptedto activate said signal means when either of said trigger circuits is inits respective second state to provide a signal prior to an exposureinterval when scene illumination is below a predetermined value, and toprovide a signal at the termination of the exposure interval to indicatethe length of the exposure interval.

1. In a camera adapted to expose film to scene light, an exposurecontrol apparatus comprising: a. photoresponsive means adapted toreceive illumination from an object scene for providing an electricalsignal that varies as a function of the level of illumination incidentthereon; b. first electronic circuit means including saidphotoresponsive means, and adapted to switch between a first statE whenthe scene illumination exceeds a predetermined level, and a second statewhen the scene illumination is below said predetermined value; c. secondelectronic circuit means including said photoresponsive means, saidsecond circuit means being activatable and adapted to switch from afirst state to a second state a period of time after activation thereof,the time period being established as a function of the level of sceneillumination; d. shutter means for covering and uncovering the exposureaperture; e. means for actuating said shutter means to uncover saidexposure aperture to initiate an exposure interval; f. means foractivating said second circuit means substantially in synchronizationwith the actuation of said shutter means to uncover said exposureaperture; g. means for actuating said shutter means to cover saidexposure aperture in response to switching of said second circuit fromsaid first state to said second state to terminate the exposureinterval, so that the exposure interval is determined by said secondcircuit means as a function of the level of scene illumination; and h.an indicator circuit including signal means, said indicator circuitbeing connected to said first and second electronic circuit means, andadapted to activate said signal means when either of said circuits is inits respective second state to provide a signal prior to an exposureinterval when the scene illumination is below a predetermined value, andto provide a signal when an exposure interval is terminated.
 2. In acamera adapted to expose film to scene light, an exposure controlapparatus comprising: a. photoresponsive means adapted to receiveillumination from an object scene for providing an electrical signalfunctionally related to the level of scene illumination incidentthereon; b. diaphragm means for establishing an exposure aperture, saiddiaphragm means including a member movable to any position along a pathto vary the size of the exposure aperture, and a magnetic memberassociated with said diaphragm member for movement therewith; c. adiaphragm control circuit including said photoresponsive means, andincluding drive coil means having oppositely poled inputs, said coilmeans being associated with said magnetic member for moving saiddiaphragm member in a first direction along said path in response toenergization of one of said drive coil inputs and for moving saiddiaphragm member in the respectively opposite direction along said pathin response to energization of the other drive coil input, said circuitbeing activatable to selectively energize said coil means to adjust theexposure aperture to a size suitable for the level of illuminationincident on said photoresponsive means; d. means for activating saiddiaphragm control circuit to adjust the exposure aperture; e. actuatableshutter means for covering and uncovering said exposure aperture; f. afirst trigger circuit including said photoresponsive means, said circuitbeing activatable and adapted to switch from a first state to a secondstate a period of time after activation of said trigger circuit, thetime period being established as a function of the position of thediaphragm member and the second electrical signal from saidphotoresponsive means; g. means for actuating said shutter means touncover said exposure aperture to initiate an exposure interval afteractivation of said diaphragm control circuit; h. means for activatingsaid first trigger circuit in synchronization with the actuation of saidshutter means to uncover said exposure aperture; i. means for actuatingsaid shutter means to cover said aperture in response to switching ofsaid first trigger circuit to its second state to terminate the exposureinterval, so that the exposure interval is determined by said firsttrigger circuit as a function of the level of scene illumination and thesize of the exposure aperture; j. a second trigger circuit includingsaid photorespoNsive means, said second trigger circuit being adapted toswitch between a first state when said electrical signal exceeds apredetermined value, and a second state when said electrical signal isbelow said predetermined value; and k. an indicator circuit includingsignal means, said indicator circuit being connected to said first andsecond trigger circuits, and adapted to activate said signal means wheneither of said trigger circuits is in its respective second state toprovide a signal prior to an exposure interval when scene illuminationis below a predetermined value, and to provide a signal at thetermination of the exposure interval to indicate the length of theexposure interval.